1. Field of the Invention
The present invention relates to a mechanism to dissipate heat from an optical transceiver, in particular, the invention relates to a structure of a heat sink provided in a cage to receive the optical transceiver.
2. Related Prior Art
An optical transceiver, which transmits and receives optical signals through an optical connector mated therewith by optically active devices of a light-emitting device and a light-receiving device each made of semiconductor materials, generally includes a body that installs a plurality of electronic components, electronic circuits and circuit boards; and an optical receptacle that receives the optical connector. One type of optical transceivers is called as a hot-pluggable optical transceiver, in which the transceiver is inserted into or removed from a cage provided on a host board to engage an electrical plug of the transceiver with an optical connector prepared in the deep end of the cage without turning off the power of the host system.
FIG. 7 schematically illustrates one type of the pluggable transceiver called as the XFP. FIG. 7 illustrates a state where the XFP transceiver is installed on the host board. A Japanese Patent Application published as JP-2007-156461A has disclosed such XFP transceiver. As illustrated in FIG. 7, on the host board 1 is provided with the cage 2 so as to expose the front end of the cage with an opening 2a from the bezel 1a of the host system. The XFP transceiver 3 is inserted into or removed from the opening 2a. In the rear end of the transceiver 3 is formed with an electrical plug 4. The transceiver 3 may electrically communicate with the host system by engaging this plug with an optical connector, not shown in the figure, provided in the deep end of the cage.
On the top of the cage 2 is provided with a heat sink 6 to dissipate heat from the transceiver 3. The clip 7 bounds the heat sink with the cage 2. The roughness of the top surface of the transceiver 3 and that of the heat sink 6, that is, the surfaces to be adhered to each other, affects the heat-dissipating efficiency.
Recent transmission speed in the optical communication system exceeds 10 Gbps and reaches 100 Gbps, which inevitably accompanies with the larger power consumption of the electronic and optical devices. An effective heat-dissipating mechanism is always required. It is inevitable to obtain the efficient heat conduction between solids, such as the contact between the housing of the transceiver and the heat sink of the cage, to widen a contact area and to make the surfaces to be contacted smooth as possible. However, the process to obtain such smooth surfaces is cost-ineffective and the outer dimensions of the transceiver do not permit the widened area.
Another method to secure the effective thermal contact between metals has been known, in which a viscous paste or a resin sheet with less hardness is put between the metals. Although the resin is inherently inferior in the thermal conductivity, it is applicable as a thermo-conducting sheet by merging metals or ceramics with good thermal conductivity in a shape of the powder and by thinning the thickness thereof as possible. Such a member, hereafter denoted as a thermo-conducting sheet, is applicable as a gap-filler put between two members rigidly fixed with respect to each other by removing air gaps and equivalently expands the contact area; accordingly, it secures the efficient heat transmission between members. However, it is insufficient for the heat transmission only to make them in contact to each other, the control of an adequate pressure applied to the members and the thermal conductivity of the thermo-conducting sheet are necessary.
In a conventional pluggable optical transceiver, the heat-dissipation has been performed only by the physical contact between the housing of the transceiver and the heat sink without any thermo-conducting sheet. In another case where the heat generation by the transceiver is comparably less, the housing of the transceiver itself may perform the heat-dissipating function without coming in contact with the heat sink. However, recent pluggable optical transceivers have generated heat more and more as the transmission speed and the transmission distance increases, which inevitably requests the heat sink and the effective heat-dissipating path from the transceiver to the heat sink.
The pluggable optical transceiver, as the name itself indicates, is inserted into or extracted from the cage. Thus, the arrangement for the thermal contact between the housing of the transceiver and the heat sink is necessary not to obstruct the insertion or the extraction of the transceiver with respect to the cage. When the transceiver is inserted into the cage, the heat sink provided in the cage must be untouched to the housing until the transceiver is set in a regular position to secure the smooth insertion. The present invention is to provide such a mechanism between the housing of the transceiver and the heat sink.